The invention discloses a dehumidifier with a multifunctional drainage function and a drainage method. The dehumidifier comprises a box body and a drainage device, wherein the drainage device comprises a water receiving tray and a water tank, a first drainage opening of the water receiving tray directly face a water inlet of the water tank, the dehumidifier further comprises a water pump, a firstconnecting piece and a second connecting piece, the water pump is arranged in the middle of the box body, the first connecting piece and the second connecting piece are arranged on the box body, a water inlet of the water pump is connected with the first connecting piece through a pipeline, a water outlet of the water pump is connected with the second connecting piece, the water tank is provided with a drainage pipe, one end of the drainage pipe extends into the bottom of the water tank, the other end of the drainage pipe is connected with a third connecting piece arranged on the water tank, the third connecting piece is in tight butt joint with the first connecting piece, and a dehumidification device and the water pump are electrically connected with an electric cabinet assembly. According to the dehumidifier and the method, the dehumidifier separates the water pump from the water tank, the water pump is prevented from being eroded by water or acid and alkali, the service life of thewater pump is prolonged, the drainage method comprises an automatic drainage mode, a manual drainage mode and a direct drainage mode, and good applicability is achieved.